1. Field of the Invention
The present invention relates to vibration actuators, and more particularly to vibration actuators to be mounted in mobile communications, such as hand-held telephones for fulfilling a function to generate ringing tones, voices and vibrations.
2. Description of the Related Art
As the conventional art, Japanese Unexamined Patent Publication (JP-A) No. H10-165892 discloses a vibration actuator for use in a pager vibration actuator. The conventional vibration actuator includes a magnetic circuit composed of a permanent magnet, a yoke and a plate. This magnetic circuit is supported by a damper and a supporting rubber having a flexible structure and grappling with claw-like projections installed on a supporting base. With this construction, the magnetic circuit is flexibly movable up and down. The conventional vibration actuator is constructed such that the magnetic circuit moves up and down along its axial directions in response to supply of a drive current to a coil 15 to transmit the vibration through an outer peripheral portion of the coil and the supporting base to the external.
In the conventional vibration actuator, in the case of sound generation, since the vibrations of an external housing (body of equipment) act principally as a sound generating source, a drawback exists in that, depending on the design and thickness of the housing, a lack of output sound pressure level occurs so that difficulty is experienced in setting a frequency characteristic arbitrarily.
In addition, as a further problem, a conventional mounting method incurs complexity of product configurations because the production configuration of the vibration actuator varies among the vibration actuator mounting modes.
Accordingly, it is an object of the present invention to provide a vibration actuator capable of setting the frequency characteristic arbitrarily while maintaining a high output sound pressure level, irrespective of the design and thickness of the external housing.
It is another object of this invention to provide a vibration actuator capable of realizing a plurality of mounting modes with one product configuration and of reducing its size while having an excellent acoustic characteristic.
It is still another object of this invention is to provide a mobile communication terminal including the foregoing vibration actuator.
According to one aspect of this invention, there is provided a vibration actuator comprising a drive section comprising a magnetic circuit with a magnetic gap and a coil placed in the magnetic gap, a vibrator driven by the drive section, an external plate member spaced from the vibrator, and a spacer disposed between the vibrator and the external plate member and having an end portion supporting a peripheral edge portion of the vibrator and an opposite end portion supporting the external plate member. The spacer is a tubular member so that a closed space is defined by the vibrator, the spacer and the external plate member to form an acoustic space based on the Helmholtz""s resonance principle.
According to another aspect of this invention, there is provided a mobile communication terminal having a housing and containing a vibration actuator in the housing, the vibration actuator comprising a drive section comprising a magnetic circuit with a magnetic gap and a coil placed in the magnetic gap, a vibrator driven by the drive section, an external plate member spaced from the vibrator, and a spacer disposed between the vibrator and the external plate member and having an end portion supporting a peripheral edge portion of the vibrator and an opposite end portion supporting the external plate member. The spacer is a tubular member so that a closed space is defined by the vibrator, the spacer and the external plate member to form an acoustic space based on the Helmholtz""s resonance principle.
In this invention, the closed space can arbitrarily be set in volume by changing the diameter of the vibrator, the height of the spacer or the diameter of the housing or the external plate member. Likewise, through holes can arbitrarily be set in area by changing its configuration/number.